Not sure what your source is but Bremen Ultras are very, very left leaning.
The club itself is also a bit more left leaning just look at the AFD statements.

In 2007 there was an attack on the antirascist Ultra Group Racaille by far right Hooligans at a party inside the stadiums east curve hall. Back at that time most fans were like you said trying to be unpolitical and to avoid any conflicts but there was also the first root of leftist fan groups and anti-rascist, anti-homophobic etc. fan groups coming up.

This attack lead to a change in our fan scene but since then the majority of our ultra scene has been very far left leaning and the Hooligan Groups have been driven out of the stadium.

Of course there is no generalisation of normal fans. I do know someone with very right wing views whos St. Pauli fan but in general our fan scene right now and especially the ultras are left leaning.